[en] The external beam audit is a part of the Quality Assurance Programme (QAP) in radiotherapy that should be carried out to check the accuracy of dose delivered by the radiotherapy treatment units are within the tolerance limit of A ± 5 % as recommended by the International Commission of Radiation Units and Measurements (ICRU) Report No. 24. In this work, thermoluminescence dosimeters (TLD) in powder form were chosen to be used in the dose quality audit for the radiotherapy treatment units in Malaysia. As a preparation, the characterizations of a new batch of TLD-100 powders were studied. The studies include checks for the response of TLD-100 before and after pre-annealing process, reproducibility and linearity of TL signal. Results show that the response of TLD-100 powder after pre-annealing increases by 65 % compared with before pre-annealing process. These TLD-100 powders also provide reliable and consistent readings for the absorbed dose to water within the range of 150 cGy to 250 cGy with the maximum standard uncertainty of 0.554 μC. Finally, the calibration curves for 6 MV and 10 MV photon beams were established. These curves will be used in determining the absorbed dose to water (Dw) from user's irradiated TLDs. The expanded uncertainty (coverage factor k=2) of Dw determination was estimated to be 4.1 %. As a conclusion, these TLD-100 powders are ready to be used as a transfer detector for evaluating the accuracy of user's delivery dose in the radiotherapy beam audit program in Malaysia. (author)

[en] A study was carried out to determine the uncertainty of the Medical Physics Group Standard Densitometer which is used to measure the Optical Density (OD) of radiographic film in Sensitometer reproducibility test. A NIST Photographic Film Step Tablet is used as Standard Reference Material (Standard Strip). It consists of 23 different optical density ranging from 0.072 to 4.024. While a Fluke Digital Densitometer is used as the standard Densitometer with 3 mm aperture. The Standard Strip OD was measured weekly to evaluate the output consistency of the Densitometer. The uncertainty calculation of the Densitometer includes the consistency and accuracy of the unit and the uncertainty of the Standard Strip. From the test results, in 2010 the unit consistency shows a maximum variation of not more than ±0.03 with combined uncertainty of not more than 0.07 (k=2), while in the year 2011 it increased to ±0.16 with combined uncertainty not more than 0.32 (k=2). The increased in uncertainty was due to the lamp malfunction of the Densitometer unit. However the maximum Standard Error between both years was not more than 1.6 %. As a conclusion, the Densitometer has a consistence output reading however the uncertainty of the output is influence by the light source (lamp). (author)

[en] The main objective of this study is to determine an equivalent decay time for each lead lined tube that will be used in linearity test (shield method) for calibration of dose calibrator. The shield method is very practical in the linearity test due to its relatively very short time of only six minutes to acquire radioactive decay until ten half-lives compared to the normal decay method that takes three days to measure the same number of readings. The equivalent decay time measurement was performed using a vial of ^99mTc with 6.007 hours half-life that was assayed in CRC-15R dose calibrator SN 258797 and lead lined tubes of calicheck kit that were inserted at a time to obtain decay readings from ^99mTc source. Using radioactive decay formula, the equivalent decay time for each lead lined tube was calculated. This measurement should be performed at least once a year to ensure the integrity of the lead lined tubes otherwise the result of linearity test will be affected. Result show that the equivalent decay time for each lead lined tube varies every year with maximum deviation of 0.7 %. (author)

[en] An inter-comparison study was conducted to compare the counting efficiency (CE) and minimum detectable activity (MDA) of thyroid monitoring systems from hospitals and Nuclear Malaysia. In this study, the CE and MDA were assessed using three standard sources of ⁵⁷Co, ¹³³Ba and ¹³⁷Cs having traceability to the National Physical Laboratory (NPL), United Kingdom. The CE and MDA were determined at a fixed measurement setup of 100 s counting time and 21 cm neck phantom - detector distance, in which the source was placed in the neck phantom. A total of 5 thyroid monitoring systems from 2 government hospitals and Nuclear Malaysia were involved in this study. The overall results of CE vary within 0.0018-0.0038 cps/ Bq, 0.0009-0.0030 cps/ Bq and 0.0003-0.0006 cps/ Bq for to ⁵⁷Co, ¹³³Ba and ¹³⁷Cs , respectively. The variations that occur may be due to differences in technical specifications and designs of the system. Although, all radionuclides of interest shows a large variation of MDA in which 45 %, 65 % and 80 % for ^57Co, ¹³³Ba and ¹³⁷Cs, respectively. All units of the thyroid monitoring system demonstrated that the MDA of ¹³³Ba was within the range of 209-894 Bq; these values are comparable with other units of the thyroid monitoring system which participated in the International Atomic Energy Agency (IAEA) intercomparison program. (author)

[en] The Medical Physics Calibration Laboratory has been accredited in accordance with MS ISO/IEC 17025 since 2013, with the scope to provide calibration service of diagnostic dosemeter, except mammography. In order to ensure continual improvement of our service, the customer satisfaction survey is carried out every year, except in 2015 where the laboratory was not operated within the ISO scope. This paper reports the results of the customer satisfaction survey from 2013 to 2020 based on approximately 33 % of customer feedbacks that we received each year. The result shows that the average customer satisfaction index from 2013 to 2020 is 81 %. From 2016 to 2020, the results are maintained more than 80 %, in which the clean working environment and counter services are always received positive feedback from the customers. Out of 5, the customers gave an average satisfaction index of 4 for the 12 criteria that are assessed in this survey. From the gap analysis, three criteria are identified to be prioritized for improvement which are handling payment efficiency, accessibility to personnel and follow-up calls. In conclusion, the laboratory is committed to taking the best corrective action incommensurate with the customer feedback to keep up our excellent service. (author)

[en] Calibration of dose calibrator is significant in order to ensure that the equipment operates optimally and provides accurate and reliable measurements of the total activity of radiopharmaceuticals before being administered into the patients. Through this work, the response between the secondary standard dose calibrator and users radioactivity measurement are obtained by using standard sources such as ⁵⁷Co, ¹³³Ba, ¹'3⁷Cs and ⁶⁰Co. The calibration procedure is in accordance with the NPLs (National Physical Laboratory, United Kingdom) document; Guide No. 93[1] and the IAEA (International Atomic Energy Agency) Technical Report Series No. 454 [2] is used as a reference for maintaining secondary standard dose calibrator. A total of 21 units of dose calibrator from eight nuclear medicine departments comprising five hospitals, two medical centres and one production laboratory were calibrated. The measurement results were inter compared with the national standard equipment and a baseline data was established for future comparison as well as dose optimization purposes. Results showed that the overall response of all dose calibrators are within NPLs tolerance limit of ±10 % except for 5 units which exceed the tolerance limit for radionuclide ¹³³Ba and ⁵⁷Co.(author)

[en] Calibration of quality control (QC) test tools used in diagnostic radiology is legally required under the Ministry of Health (MOH) requirement. The Medical Physics Calibration Laboratory of the Malaysian Nuclear Agency is the national focal point for the calibration of quality control test tools used in diagnostic radiology. The Medical Physics Calibration Laboratory has measurement traceability to primary standard dosimetry laboratory (Physikalisch-Technische Bundesanstalt (PTB)), thus providing an interface between the primary standard dosimetry laboratory and Malaysian hospitals, clinics and license class H holder. The Medical Physics Calibration Laboratory facility is comprised of a constant potential x-ray system with a capability of 160 kV tube and a series of reference and working standard ion chambers. The stability of reference and working standard ion chambers was measured using strontium-90. Dosimetric instruments used in diagnostic radiology is calibrated in terms of air kerma to comply with an International Code of Practices of dosimetry for example IAEA's Technical Report Series number 457. The new series of standard radiation qualities was established based on ISO/IEC 61267. The measurement of beam homogeneity was measured using film and ion chamber to define the field size at certain distance and kV output was measured using the spectrometer and non-invasive kVp meter. The uncertainties measurement was determined with expended uncertainties to a level of confidence of approximately 95% (coverage factor k=2). This paper describes the available facility and the effort of the Medical Physics Calibration Laboratory to upgrade the laboratory towards ISO/IEC 17025. (author)

[en] Routine assessment of internal contamination for potential exposed radiation workers is essential to be carried to ensure dose received by the workers are adhered the annual dose limits of 20 mSv as stated in the Basic Safety Radiation Protection (BSRP) 2010 as well as to verify the applications of radiation protection principles in the work place. For monitoring intake of ¹³¹I radionuclide by the workers, a direct measurement technique using Captus 3000 Thyroid Counter System could be used. In Medical Physics Group, this equipment is calibrated and maintained with two types of gamma emitter radionuclides; ¹³⁷Cs and ¹⁵²Eu. In order to ensure consistent and reliable measurement, a quality assurance consists of linearity, constancy and chi-square tests have been implemented on weekly basis to the thyroid system. In addition, annual checks on minimum detectable activity (MDA) and efficiency for several radionuclides also have been performed. The results shows that all QA tests were complied the tolerance limits given the manufacturer. The MDA value for ¹³¹I radionuclide was determined to be 149.2 ± 35.4 Bq and the efficiency values for the selected radionuclides were comparable with thyroid counters in other institutions. As a conclusion, the equipment now is fully operational and could be used for routine internal monitoring of exposed personnel. (author)

[en] The objective of this study is to perform a thermoluminescent dosimetry (TLD) postal dose quality audit for megavoltage X-ray teletherapy units in Malaysia. This audit is essential to be carried out to ensure adequate precision in the dosimetry of clinical beams before being delivered to the patients. Through this work, participating centres were requested to irradiate three capsules of TLD-100 powder with an absorbed dose to water of 2 Gy for 6 MV and 10 MV photon beams. The International Atomic Energy Agency (IAEA)s Technical Report Series No. 398 is used as a reference standard for TLD irradiation. A total of 22 photon beams from ten radiotherapy centres comprising one government hospital and nine private medical centres were evaluated. The percentage deviation of users measured absorbed dose relative to Secondary Standard Dosimetry Laboratory (SSDL) mean absorbed dose was calculated. The results showed that all photon beams are within the IAEA acceptance limit of ±5 % except six photon beams. These centres were followed up with a second round of TLD irradiation which resulted in a better compliance. As a conclusion, regular audits should be performed to ensure consistency of radiotherapy treatment unit performances thus maintaining the accuracy of dose delivered to patients in all radiotherapy centres in Malaysia. (author)